Devices such as industrial paper making machines require continuous lengths of woven fabric to provide, for example, forming fabrics, drying webs and pressing felts and other industrial fabrics. To form a continuous length, opposite ends of a length of fabric must be joined together. Also, shorter lengths of fabric can be joined by seams to form a longer length of fabric,
Generally, a woven scam is preferred, because it provides a smoother, flatter join which is important in many applications, such as paper making. In order to weave the ends of fabric together in a seam, weft, or lateral, threads are removed from each fabric end in a process called unravelling to expose a section of warp, or longitudinal, threads called a fringe. The fringes of the ends of the fabric to be joined are then overlayed and the warp yarns are reentered, or rewoven, to form the seam.
The formation of the seam is generally an automated reweaving process. However, it is difficult and time consuming to prepare fringes for the seaming process. Typically, the unravelling of a fabric to prepare a fringe is performed manually, in a time consuming and labour intensive process. Usually, the manual preparation of fabric edges is performed on fringe preparation tables where an operator manually cuts short sections of the weft threads and then pulls these sections out of the fabric.
The fabric used in commercial paper making machines may be 30 feet, or more, in width. In addition to the time and labour required to unravel such fabric to provide a fringe, the repetition and monotony of the unravelling operation can lead to repetitive stress injuries in the workers preparing the fringes. Additionally, if the sections of cut weft thread are too long, or the force used to pull them out is too great, the underlying warp threads can be damaged, resulting in discontinuities in the eventual seam. In addition, the crimp, or deformation of the warp threads can be destroyed, making it difficult to reenter the warp threads to create the woven seam.
U.S. Pat. No. 4,736,499, entitled "Equipment for Unravelling Threads from a Fabric", to Kopcke, describes a device which attempts to automate the unravelling process to provide a fringe suitable for spiral seaming. Spiral seaming involves the insertion of a plastic spiral into a narrow fringed channel across the width of the two ends to be joined. In this device, an unravelling unit using vertically reciprocating needles in combination with a cutter, pulls out and cuts sections of weft thread. The unit travels across the width of the fabric unravelling a number of threads which corresponds to the number of needles used.
However, problems exist in the device taught by Kopcke in that it can only remove a number of weft threads equal to the number of needles provided. If a wider fringe is desired, the unit must be repositioned and the unravelling process repeated across the entire width of the fabric. Further, while a narrow fringe, typically only two to ten threads in width, is sufficient for spiral seaming, a woven scam typically requires the fringe to be from about 1" to about 10" in width, which may necessitate the removal of hundreds of weft threads. With the Kopcke device, many passes of the device across the fabric would be required.
In addition, Kopcke employs a mechanical sensor, following the channel between two adjacent weft threads, to ensure straight tracking of the unravelling unit. Accordingly, the equipment may not track properly across fabrics with a tight weave, or with modern fabrics which have a more complex, multi-layered weave. As well, since Kopcke employs a trailing cutter to cut the pulled treads after they have been released by the needles, it may not function adequately on soft-fibred fabrics, as soft threads may not be stiff enough to maintain their position as the cutter is moved into them.